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Iris Patterns
Human Iris Pattern GWAS The iris of your eye is the circular portion surrounding the pupil. Much like fingerprints, the patterns displayed in the iris of your eye are diverse and unique to individuals. Due to this it is possible to use iris recognition as a form of identification. Until recently, a limited amount of information was known about the genetic basis of iris patterns. In light of this, a GWAS on iris patterns was performed by scientists in Australia on roughly 2,700 people of European decent. Three iris characteristics, crypts, pigmented rings and furrow contractions, were measured and observed on each individual in the study and the genetic basis behind their diversity was brought to light. Crypts are the oval-shaped areas in your iris that represent the openings in your iris. The researchers in the GWAS found a single SNP associated with the presence of crypts in the iris. The SNP in question is located near the SEMA3A gene. SEMA3A encodes a protein that acts on the iris as well as the brain and directs cell movement. Interestingly, mutations in SEMA3A have been found previously to be associated with neurological conditions such as Alzheimer's and schizophrenia. Furrow contractions are the circular and radial bands within the iris. These are the result of the iris folding in the exact same way each time it expands or contracts due to changes in light intensity. An SNP located within the cytoskeleton gene TRAF3IPI was found to be associated with variations in furrow contractions. These findings indicated that TRAF3IPI likely controls the overall thickness and density of the iris. It is also essential for cytoskeleton function. Additionally mutations in TRAF3IPI have been associated with neurogenesis, neural migration and synaptogenesis. A third SNP found to be housed near the SLC24A4 gene has been connected to pigmented rings. These are differently colored rings around the pupil of the eye. Pigment rings are the main cause of differences in pigmentation between green and hazel eyes. SLC2A4A has previously been determined as the determining factor between green and brown vs. blue eyes. Pigmentation rings on blue irises have been found to cause the pigment to appear green or hazel. Due to this, researchers hypothesize that the presence or absence of pigmented rings could be the driving force behind variation in eye color. The study also reported several interesting trends in variation based on sex and age of the individual. Older participants were found to have more furrow contractions and pigmented spots on the iris than younger members of the study. Males tended to possess more crypts than females, however females were found to have more pigmented spots, furrow contractions and pigmentation rings than males. The study concluded that iris patterns are closely linked to the brain. The close genetic linkage between the iris and the brain would account for the distinct appearance of humans iris's as brains are highly unique to individuals. Reference Mats Larsson, D. L. D., Gu Zhu, Jimmy Z. Liu, Stuart Macgregor, Allan F. McRae, MAragaret J. Wright, Richard A. Sturm, David A. Mackey, Grand W. Montogmery, Nicholas G. Martin and Sarah E. Medland. (2011). GWAS Findings for Human Iris Patterns: Associations with Variants in Genes that Influence Normal Neuronal Pattern Development American Journal of Human Genetics 89(2), 334-343.